/**
 * @file distanceDemo.c
 * @author your name (you@domain.com)
 * @brief 通过两个点的横、纵坐标，求线段长度
 * @version 0.1
 * @date 2022-11-15
 * 
 * @copyright Copyright (c) 2022
 * 
 */
double distance(double x1,double y1,double x2,double y2);
int main(){
    double x1,y1,x2,y2;
    scanf("%f%f%f%f",&x1,&y1,&x2,&y2);
    printf(("The distance is %f",distance(x1,y1,x2,y2)));
    return 0;
}
double distance(double x1,double y1,double x2,double y2)
{
    return sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1));
}